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Showing papers in "IEEE Communications Letters in 2009"


Journal ArticleDOI
TL;DR: This letter evaluates performance of polar codes designed with the new construction method, and compares it with that of the codes constructed with another heuristic method with linear complexity proposed by Arikan.
Abstract: Polar coding, proposed by Arikan, makes it possible to construct capacity-achieving codes for symmetric binary-input discrete memoryless channels, with low encoding and decoding complexity. Complexity of the originally proposed code construction method, however, grows exponentially in the block-length unless a channel is the binary erasure channel. Recently, the authors have proposed a new capacity-achieving code construction method with linear complexity in the block-length for arbitrary symmetric binary-input memoryless channels. In this letter, we evaluate performance of polar codes designed with the new construction method, and compare it with that of the codes constructed with another heuristic method with linear complexity proposed by Arikan.

449 citations


Journal ArticleDOI
TL;DR: This letter quantifies the temporal and spatial correlation of the interference in a wireless ad hoc network whose nodes are distributed as a Poisson point process on the plane when ALOHA is used as the multiple-access scheme.
Abstract: Interference is a main limiting factor of the performance of a wireless ad hoc network The temporal and the spatial correlation of the interference makes the outages correlated temporally (important for retransmissions) and spatially correlated (important for routing) In this letter we quantify the temporal and spatial correlation of the interference in a wireless ad hoc network whose nodes are distributed as a Poisson point process on the plane when ALOHA is used as the multiple-access scheme

274 citations


Journal ArticleDOI
TL;DR: This paper presents the performance of fixed decode-and-forward cooperative networks with relay selection over independent but not identically distributed Nakagami-m fading channels, with integer values of the fading severity parameter m.
Abstract: In this paper, we present the performance of fixed decode-and-forward cooperative networks with relay selection over independent but not identically distributed Nakagami-m fading channels, with integer values of the fading severity parameter m. Specifically, closed-form expressions for the symbol error probability and the outage probability are derived using the statistical characteristic of the signal-to-noise ratio. We also perform Monte-Carlo simulations to verify the analytical results.

183 citations


Journal ArticleDOI
TL;DR: This paper derives an expression for the limiting eigenvalue ratio distribution, which turns out to be much more accurate than the previous approximations also in the non-asymptotical region, and is applied to calculate the decision sensing threshold as a function of a target probability of false alarm.
Abstract: Recent advances in random matrix theory have spurred the adoption of eigenvalue-based detection techniques for cooperative spectrum sensing in cognitive radio. These techniques use the ratio between the largest and the smallest eigenvalues of the received signal covariance matrix to infer the presence or absence of the primary signal. The results derived so far are based on asymptotical assumptions, due to the difficulties in characterizing the exact eigenvalues ratio distribution. By exploiting a recent result on the limiting distribution of the smallest eigenvalue in complex Wishart matrices, in this paper we derive an expression for the limiting eigenvalue ratio distribution, which turns out to be much more accurate than the previous approximations also in the non-asymptotical region. This result is then applied to calculate the decision sensing threshold as a function of a target probability of false alarm. Numerical simulations show that the proposed detection rule provides a substantial improvement compared to the other eigenvalue-based algorithms.

180 citations


Journal ArticleDOI
J. van de Beek1, Fredrik Berggren1
TL;DR: A new OFDM signalling format characterized by a precoder that renders the emitted signal's phase and amplitude continuous achieves superior out-of- band power characteristics at the price of a slightly reduced receiver sensitivity.
Abstract: In this letter we report a new OFDM signalling format characterized by a precoder that renders the emitted signal's phase and amplitude continuous. It achieves superior out-of- band power characteristics at the price of a slightly reduced receiver sensitivity.

175 citations


Journal ArticleDOI
TL;DR: This letter will provide the proof which verifies that OSP is optimal for both amplify-and- forward (AF) and decode- and-forward (DF) relay links when optimal power allocation is applied.
Abstract: We consider a two-hop relay link in which orthogonal frequency division multiplexing (OFDM) is used on both hops. Under a joint sum-power constraint, our aim is to allocate power over subcarriers on the two hops such that the instantaneous rate of the relay link is maximized. Ordered subcarrier pairing (OSP) has been proposed in the literature to further improve the relay link rate; however, the optimality of OSP has been proven only for equal power allocation and the proof of its optimality under optimal power allocation has not been available yet. In this letter, we will provide our proof which verifies that OSP is optimal for both amplify-and-forward (AF) and decode-and-forward (DF) relay links when optimal power allocation is applied.

164 citations


Journal ArticleDOI
TL;DR: The performance of a two hop amplify-and-forward relay system, where the source-relay and the relay-destination channels experience Rayleigh and Rician fading respectively, is investigated and exact and lower bound expressions for the outage probability and average bit error probability are derived.
Abstract: The performance of a two hop amplify-and-forward relay system, where the source-relay and the relay-destination channels experience Rayleigh and Rician fading respectively, is investigated. We derive exact and lower bound expressions for the outage probability and average bit error probability, where the bounds become tight at high signal-to-noise ratios (SNR). Our results are verified through comparison with Monte Carlo simulations, where we also illustrate the positive impact of the Rician factor on the system performance.

160 citations


Journal ArticleDOI
TL;DR: Although EEE improves the energy efficiency, there is still potential for substantial further energy savings as in many cases most of the energy is wasted in waking up and sleeping the link.
Abstract: Until very recently, energy efficiency has received little attention in many wired communications environments. For example, in most current Ethernet standards the transmitter and receiver operate at full power even when no data is being sent. However, new upcoming energy-aware standards, such as Energy Efficient Ethernet (EEE), are addressing this issue by introducing a low power mode for idle link intervals. The future EEE standard defines the procedure to enter and exit the low power mode. With EEE the actual energy savings will depend on the amount of traffic and on the timing of the frame arrivals. In this paper the performance of EEE in terms of energy saving is evaluated. The results show that although EEE improves the energy efficiency, there is still potential for substantial further energy savings as in many cases most of the energy is wasted in waking up and sleeping the link.

144 citations


Journal ArticleDOI
TL;DR: A squared distance criterion for antenna location design in generalized distributed antenna systems (GDAS) is proposed to maximize the cell averaged ergodic capacity and is equivalent to codebook design in vector quantization.
Abstract: A squared distance criterion for antenna location design in generalized distributed antenna systems (GDAS) is proposed to maximize the cell averaged ergodic capacity. The criterion requires the antenna port locations minimize the expectation of the squared distance between a randomly distributed user and the nearest antenna port. This is equivalent to codebook design in vector quantization. For uniform user distribution, we can easily derive analytical expressions for antenna locations. For more general user distribution, we can obtain numerical results using the codebook design algorithm. Applying the proposed criterion to circular-layout GDAS with uniform user distribution and linear cell with non-uniform user distribution, we achieve near optimal performance.

123 citations


Journal ArticleDOI
J. van de Beek1
TL;DR: A novel spectrum-sculpting precoder flexibly suppresses emitted power in predefined parts of the spectrum by tens of decibels, suitable in cognitive OFDM systems where the emitted signal's spectrum is adapted to time-varying reigning radio circumstances.
Abstract: A novel spectrum-sculpting precoder flexibly suppresses emitted power in predefined parts of the spectrum by tens of decibels. The precoder is particularly suitable in cognitive OFDM systems where the emitted signal's spectrum is adapted to time-varying reigning radio circumstances.

120 citations


Journal ArticleDOI
TL;DR: The moment generating function (MGF) is evaluated for the probability density function characterizing this new channel model and the derived MGF expression is used in evaluating the bit error rate for different coherent modulation techniques over this generalized fading channel.
Abstract: In this letter, we consider the alpha - mu channel fading model and we evaluate the moment generating function (MGF) for the probability density function characterizing this new channel model. The derived MGF expression is used in evaluating the bit error rate for different coherent modulation techniques over this generalized fading channel. We also derive an expression for the outage probability for this channel model. All the derived expressions are in closed forms and general that can reduce to the well known fading channel distributions in the literature such as Rayleigh, Nakagami-m, and Weibull model as special cases.

Journal ArticleDOI
TL;DR: The model is used to quantify the vulnerability of the two relaying schemes to node selfishness but also drive remediation actions against it, suggesting that the performance advantage of unrestricted relaying over two-hop relaying decreases both with the number of selfish nodes and the intensity of their selfishness.
Abstract: Delay tolerant networks rely on the mobility of their nodes and sequences of their contacts to transfer data. Proposed data forwarding mechanisms represent different trade offs between data transfer speed and network resource consumption, most of them assuming perfect cooperation among network nodes. Nevertheless, nodes may exhibit selfish behavior, in particular when they are constrained with respect to energy, computational power, and/or storage space. In this paper, we analytically assess the performance of two popular data relaying alternatives, the unrestricted and two-hop relay schemes, when nodes behave selfishly while forwarding data. Our results suggest that the performance advantage of unrestricted relaying over two-hop relaying decreases both with the number of selfish nodes and the intensity of their selfishness, irrespective of whether nodes defer from relaying deterministically or probabilistically. We use our model to quantify the vulnerability of the two relaying schemes to node selfishness but also drive remediation actions against it.

Journal ArticleDOI
TL;DR: Proposed algorithm can achieve much better classification accuracy in distinguishing BPSK from complex-valued modulation techniques, under real-world channel propagation conditions.
Abstract: An automatic modulation classification algorithm for application in communications via multipath fading channels, without a priori information on channel characteristics, based on normalized sixth-order cumulants is described. In comparison with existing approaches, proposed algorithm can achieve much better classification accuracy in distinguishing BPSK from complex-valued modulation techniques. Theoretical analysis is verified via extensive simulations, under real-world channel propagation conditions.

Journal ArticleDOI
TL;DR: In this paper, tight closed-form approximations for the ergodic capacity of dual-hop fixed-gain relaying systems are derived for independent Nakagami-m fading channels, with partial relay selection being employed in the first-hop transmission.
Abstract: In this Letter, tight closed-form approximations for the ergodic capacity of dual-hop fixed-gain relaying systems are derived. Our analysis allows for independent Nakagami-m fading channels, with partial relay selection being employed in the first-hop transmission. Simulation results are presented in order to confirm the accuracy of the proposed approximations. It is noteworthy that our formulations can be easily extended for the outage capacity analysis and guidelines for such are provided.

Journal ArticleDOI
TL;DR: This letter addresses a coverage problem through the use of a self-deployed mobile wireless sensor network by proposing a distributed motion coordination algorithm to autonomously form a sensor barrier between two given landmarks to achieve the barrier coverage.
Abstract: This letter addresses a coverage problem through the use of a self-deployed mobile wireless sensor network. We propose a distributed motion coordination algorithm for the mobile sensors to autonomously form a sensor barrier between two given landmarks to achieve the barrier coverage. The algorithm is developed based on some simple rules that are computationally efficient and require less communication overhead.

Journal ArticleDOI
TL;DR: Preliminary experiments and analysis indicate that the proposed chaotic model can accurately and effectively detect DDoS attack traffic and has the potential to not only detect attack traffic during transit, but to also filter it.
Abstract: DDoS attack traffic is difficult to differentiate from legitimate network traffic during transit from the attacker, or zombies, to the victim. In this paper, we use the theory of network self-similarity to differentiate DDoS flooding attack traffic from legitimate self-similar traffic in the network. We observed that DDoS traffic causes a strange attractor to develop in the pattern of network traffic. From this observation, we developed a neural network detector trained by our DDoS prediction algorithm. Our preliminary experiments and analysis indicate that our proposed chaotic model can accurately and effectively detect DDoS attack traffic. Our approach has the potential to not only detect attack traffic during transit, but to also filter it.

Journal ArticleDOI
TL;DR: A new and accurate approach to compute the bit-error-rate (BER) performance of coherent and non-coherent chaos-based communication systems and takes into account that the bit energy is varying from one transmitted bit to another.
Abstract: The aim of this paper is to present a new and accurate approach to compute the bit-error-rate (BER) performance of coherent and non-coherent chaos-based communication systems. The approach explores the dynamical properties of chaotic sequences and takes into account that the bit energy is varying from one transmitted bit to another. Compared with other widely used approaches in the literature, the proposed methodology gives accurate results even for low spreading factors.

Journal ArticleDOI
Hakyong Kim1
TL;DR: The main idea of the proposed algorithm is to reply with multiple acknowledgement packets to a single ranging request to reduce the number of packets used in ranging process and improves the ranging accuracy at the same time.
Abstract: In this letter we propose a novel ranging algorithm for the asynchronous location positioning system. The main idea of the proposed algorithm is to reply with multiple acknowledgement packets to a single ranging request. The ranging algorithm reduces the number of packets used in ranging process and improves the ranging accuracy at the same time.

Journal ArticleDOI
TL;DR: This work proposes an improved algorithm for decoding LT codes using Gaussian elimination that performs useful processing at each coded packet arrival thus distributing the decoding work during all packets reception, obtaining a shorter actual decoding time.
Abstract: We propose an improved algorithm for decoding LT codes using Gaussian elimination. Our algorithm performs useful processing at each coded packet arrival thus distributing the decoding work during all packets reception, obtaining a shorter actual decoding time. Furthermore, using a swap heuristic the decoding matrix is kept sparse, decreasing the cost of both triangularization and back-substitution steps.

Journal ArticleDOI
TL;DR: Simulation results show that significant improvement of the cooperative spectrum sensing gain is achieved by the enhanced scheme, which utilizes the signal to noise ratios to evaluate the degree of reliability of each local spectrum sensing terminal on a distributed Cognitive Radio network.
Abstract: This letter proposes an enhanced scheme for cooperative spectrum sensing which utilizes the signal to noise ratios to evaluate the degree of reliability of each local spectrum sensing terminal on a distributed Cognitive Radio network. The terminals' reliability weight is applied to adjust its sensing data more accurately before making fusion by Dempter-Shafer theory of evidence. Simulation results show that significant improvement of the cooperative spectrum sensing gain is achieved by our scheme.

Journal ArticleDOI
TL;DR: A new loss model for cognitive radio spectrum access with finite user population is presented and exact solution for the model and its approximation for computation scalability are given.
Abstract: A new loss model for cognitive radio spectrum access with finite user population are presented, and exact solution for the model and its approximation for computation scalability are given. Our model provides the investigation of the delay performance of a cognitive radio system. We study the delay performance of a cognitive radio system under various primary traffic loads and spectrum band allocations.

Journal ArticleDOI
TL;DR: This letter analyzes the performance of repetition-based cooperative wireless networks using amplify-and forward relaying and derives a close-form average SER when m is an integer, showing that the derived error rates are tight approximations particularly at medium and high SNR.
Abstract: This letter analyzes the performance of repetition-based cooperative wireless networks using amplify-and forward relaying. The network consists of a source, R parallel relays, and a destination, and the channel coefficients are distributed as independent, non-identical, Nakagami-m. The approximated average symbol error rate (SER) is investigated. For sufficiently large SNR, this letter derives a close-form average SER when m is an integer. The simplicity of the asymptotic results provides valuable insights into the performance of cooperative networks and suggests means of optimizing them. We also use simulation to verify the analytical results. Results show that the derived error rates are tight approximations particularly at medium and high SNR.

Journal ArticleDOI
TL;DR: Chang et al.'s scheme cannot provide secure key establishing service since an adversary can recover the identity of a mobile user by performing one of the attacks.
Abstract: Recently, Chang, Lee, and Chiu proposed an enhanced anonymous authentication scheme which permits mobile users to anonymously enjoy roaming service in global mobile networks. In this letter, we show that their scheme fails to achieve the anonymity by providing four attack strategies. Moreover, we show that anyone can recover a mobile user's session keys by using the identity of the mobile user. Hence, Chang et al.'s scheme cannot provide secure key establishing service since an adversary can recover the identity of a mobile user by performing one of our attacks.

Journal ArticleDOI
Jung-Min Moon1, Dong-Ho Cho1
TL;DR: Numerical analysis reveals that the proposed algorithm yields a higher probability that the user will be correctly assigned to the femto cell while maintaining the number of handoffs at the same level.
Abstract: To improve indoor coverage and network capacity, the use of hierarchical macro/femto cell networks is regarded as the most promising approach. We present an efficient handoff algorithm to support the inbound mobility from macro cells to femto cells under the consideration of large asymmetry in the transmit power of the cells. Numerical analysis reveals that the proposed algorithm yields a higher probability that the user will be correctly assigned to the femto cell while maintaining the number of handoffs at the same level.

Journal ArticleDOI
TL;DR: It is claimed that some of the expressions, results and the conclusion of X. Zhu et al., (2007) are not correct.
Abstract: We claim that some of the expressions, results and the conclusion of X. Zhu et al., (2007) are not correct. The correct expressions, results and conclusion are discussed in this letter.

Journal ArticleDOI
TL;DR: Simulation results demonstrate that the proposed precoding scheme can suppress the sidelobes significantly in contrast to the uncoded schemes, and the bit-error-rate (BER) performance of the precoded system over multipath fading channel is improved due to the frequency diversity.
Abstract: In spectrum pooling scenario, the spectral leakage of DFT-based OFDM signal can be divided into in-band-out-of-subband (IBOSB) radiation and out-of-band (OOB) radiation. A precoding scheme is proposed to suppress the IBOSB sidelobes. The precoding design is based on the generalized eigenvalue problem. Simulation results demonstrate that the proposed scheme can suppress the sidelobes significantly in contrast to the uncoded schemes. At the same time, the bit-error-rate (BER) performance of the precoded system over multipath fading channel is improved due to the frequency diversity.

Journal ArticleDOI
TL;DR: Simulation results show that the proposed algorithm yields good performance improvement in terms of sidelobe suppression, and does not have a significant impact on the peak-to-average power ratio (PAPR).
Abstract: In this letter, a new method for sidelobe suppression in non-contiguous orthogonal frequency division multiplexing (NC-OFDM) systems is proposed. Unlike the conventional approach, sidelobes are suppressed by iteratively adjusting the constellation points for the subcarriers that are close to the edges of the used bandwidth. The constellation points corresponding to the maximum sidelobe suppression are chosen for transmission. Simulation results show that the proposed algorithm yields good performance improvement in terms of sidelobe suppression, and does not have a significant impact on the peak-to-average power ratio (PAPR).

Journal ArticleDOI
TL;DR: An RF-based localization system that works using a single anchor node that is equipped with a switched-beam directional antenna that is installed on the ceiling of a room and collects signal strength information sufficient for absolute 2D target positioning.
Abstract: We propose an RF-based localization system that works using a single anchor node. The anchor is equipped with a switched-beam directional antenna that is installed on the ceiling of a room and collects signal strength information sufficient for absolute 2D target positioning. Indoor measurements are used to show satisfactory localization results with range-free (proximity), range-based and fingerprinting schemes.

Journal ArticleDOI
TL;DR: This letter proposes a novel method to estimate large-scale IP traffic matrix by using the Generalized Autoregressive Conditional Heteroscedasticity (GARCH) to model the Origin-Destination flows, which does not only hold the lower estimation errors but also is more robust to the noise.
Abstract: This letter proposes a novel method to estimate large-scale IP traffic matrix (TM). By using the Generalized Autoregressive Conditional Heteroscedasticity (GARCH) to model the Origin-Destination (OD) flows, we can easily get rid of the ill-posed problem of large-scale IP TM. Compared with previous methods, our method does not only hold the lower estimation errors but also is more robust to the noise.

Journal ArticleDOI
Howon Lee1, Dong-Ho Cho1
TL;DR: This letter analyzes a voice over IP (VoIP) capacity in a cognitive radio system as a two-dimensional discrete time Markov chain (DTMC) and describes the VoIP traffic and wireless channel as a Markov modulated Poisson process (MMPP) and Markov channel model, respectively.
Abstract: In this letter, we analyze a voice over IP (VoIP) capacity in a cognitive radio system. We formulate the system as a two-dimensional discrete time Markov chain (DTMC). The VoIP traffic and wireless channel in the cognitive radio system are described as a Markov modulated Poisson process (MMPP) model and a Markov channel model, respectively. We demonstrate various numerical and simulation results, such as packet dropping probability and VoIP capacity.